EP0991859B1 - Method and device for regulating internal combustion engines - Google Patents

Abstract

The invention relates to a method and device for regulating internal combustion engines to take into account the air humidity, especially in automobiles, by means of at least one temperature sensor (1) and a sensor (2) for directly or indirectly detecting the relative air humidity phi . According to the invention, a correction factor (a) is determined. The quantity of fuel supplied to the internal combustion engine is then adjusted according to said correction factor. The total pressure p of the humid air is optionally taken as constant or detected additionally.

Description

The invention relates to a method and a device for controlling a Internal combustion engine in a damp environment.

In general, when tuning engines, the water vapor content of the little attention was paid to the air sucked in because under normal tuning conditions The temperature of the air is low and the water vapor content in the air is negligible is small. During operation at high air temperatures and high humidity, such as For example, in tropical climates, the water vapor content in the air increases orders of magnitude that can no longer be neglected. This can lead to that for the tuning of the fuel mass supplied to the internal combustion engine increases by more than 10% is high. This error occurs in vehicles with petrol engines with control automatically adjusted, but this takes a certain time and due to the large control range leads to inaccuracies. In contrast, with diesel engines such a regulation entirely. Therefore, a default setting is used for diesel engines made either for maximum performance or minimum emission. To the diesel engine can be set to maximum humidity, but this too Loss of performance leads, or there is increased at higher air humidity Soot formation.

EP 509 496 B1 discloses a control device for a gas turbine burner for achieving stable combustion with limited NO _x emissions, comprising a device for measuring a property of the fresh air, namely the temperature and / or the humidity, and a device for correcting the fresh air Flow rate or the ratio of fuel flow rate to fresh air flow rate corresponding to the change in the measured property so that the operating point of the burner is kept in a stable combustion range, with further means for the prior determination and storage of a boundary line for stable combustion between the stable combustion area and an unstable combustion area in a coordination level of the fresh air flow rate and / or the ratio of fuel flow rate to fresh air flow rate and the temperature and / or humidity of the fresh air for each turbine load and a device for determining the instantaneous working point of the burner is provided in these coordinates, the absolute humidity of the fresh air preferably being measured. A disadvantage of the known control device is that it is relatively complex since various characteristic curves have to be determined in advance and the intended control process, which is controlled by a microprocessor, is very complex.

DE 44 40 796 A1 describes a method and a device for suction and Admixing at least one additive into a fluid flow, in particular of fresh air in a fuel flow, the additive passing through a negative pressure generated by the fluid flow when intimately mixed with the Fluid is sucked in. For this purpose it is provided that the moisture content or the relative The moisture content of the additive must be reduced before mixing Reduce pollutant exchange. The apparatus is disadvantageous in terms of apparatus Effort that complicates the use especially in motor vehicles.

Furthermore, from US-A-5,586,524 is an intake system of a two-stroke internal combustion engine known with a temperature sensor, a humidity sensor and a Pressure sensor. The data from these sensors are used in the control unit to calculate the Fuel injection quantity used.

The invention is therefore based on the technical problem, a method and a To create a device for controlling internal combustion engines, by means of which a simple adjustment of the internal combustion engine taking into account the air humidity is possible.

The solution to the technical problem results from the features of the claims 1 and 3.

By determining a correction factor from the recorded values for the temperature and the relative humidity, which means the amount of fuel to the outside Environmental parameters or the available oxygen mass is adjusted reduced emissions and fuel consumption without sacrificing performance. Furthermore, complex control devices can be dispensed with and instead of of which a controller can be used.

Further advantageous embodiments of the invention result from the subclaims.

The invention is explained in more detail below on the basis of a preferred exemplary embodiment explained. The single figure shows a schematic block diagram of the device for Control of a motor vehicle engine.

The device for control comprises a temperature sensor 1, a sensor 2 for detecting the relative humidity, a pressure sensor 3, a storage element 4 and a control device 5. The motor vehicle engine comprises an engine block 6, in which the individual cylinders are arranged, an air intake 7, a downstream air filter 8, an intake manifold 9, an intake tract 10, air inlets 11 for the individual cylinders and an exhaust pipe 12. In addition, a fuel line is provided, with an injection system 13 controlling the amount of fuel individually for each cylinder. The temperature sensor 1, the sensor 2 and the pressure sensor 3 are arranged in front of the air intake 7 and each detect temperature T _{f L} , relative humidity and the total pressure p of the humid air. The detected temperature T _{f L} is transferred to the storage element 4, in which a function of the saturation pressure of the water vapor p "(T _{f L} ) is filed. The measured temperature T _{f L} associated saturation pressure of water vapor p "(T _{f L} ), detected relative humidity and the total pressure p are in the control unit 5 to a correction factor F _{f L} summarized according to the following relationship: F f L = 1 - p "(T f L ) p * ϕ

This correction factor F _{f L} is transferred to the injection system 13 and multiplied there by a nominated injection time, so that the amount of fuel supplied to the cylinders is also adapted accordingly. About the correction factor F _{f L} the amount of fuel supplied to the cylinder is adapted to the amount of oxygen present, which is dependent on the air humidity. Since the pressure sensor 3 measures the air pressure, an air pressure meter, which is usually already present, can take over its task for the height correction. Alternatively, the temperature sensor 1, the sensor 2 and the pressure sensor 3 can also be arranged behind the air filter 8 or in the intake tract 10.

Aus der Beziehung für die allgemeine Gaskonstante R = RfL * MfL = RL * ML läßt sich dann das Verhältnis der Gaskonstante von trockener zu feuchter Luft berechnen. Das Massenverhältnis von Wasserdampf zu trockener Luft wird ebenfalls über die Substanzmengen und deren Molmassen ausgedrückt mD mL = nD nL * MD ML = ξ * MD ML wobei n_L / n_D = ξ molares Feuchteverhältnis [Mol_D / Mol_L] genannt wird, das über die relative Feuchte der Luft errechenbar ist. Es gilt ξ = ϕ * p"(TfL )p - ϕ * p"(TfL ) mit den am gleichen Ort zu bestimmenden Größen

ϕ =

relative, Luftfeuchte

p =

(Gesamt-) Druck der feuchten Luft und

p"(T_fL ) =

Sättigungsdruck des Wasserdampfes für die am Ort herrschende Temperatur der feuchten Luft T_fL .

The derivation of the correction factor F _{f L} explained in more detail. This is the expression F f L = R L R f L * 1 1 + m D / m L investigated, which describes the influence of air humidity on the dry air mass available for reaction in the cylinder. Mean
R = gas constant,
m = mass
and the indices stand here and below for
f _L = moist air
L = dry air and
D = water vapor.
The following applies to the total mass of moist air m f L = m L + m D , This can also be expressed with the molecular weights M _i and the substance amounts n _i as n f L × M f L = n L * M L + n D * M D or with the molar proportions v _i M f L = v L * M L + v D * M D , Since the sum of all molar parts of a gas mixture is equal to 1, this results in the molar part of the dry air v L = 1 - v D . so that the ratio of the molar masses of moist to dry air can also be written

From the relationship for the general gas constant R = R f L * M f L = R L * M L the ratio of the gas constant of dry to moist air can then be calculated. The mass ratio of water vapor to dry air is also expressed in terms of the amounts of substances and their molar masses m D m L = n D n L * M D M L = ξ * M D M L where n _L / n _D = ξ molar moisture ratio [mol _D / mol _L ] is called, which can be calculated from the relative humidity of the air. It applies ξ = ϕ * p "(T f L ) p - ϕ * p "(T f L ) with the sizes to be determined in the same place

ϕ =

relative humidity

p =

(Total) pressure of the humid air and

p "(T _{f L} ) =

Saturation pressure of the water vapor for the local temperature of the humid air T _{f L} ,

If the mole fraction of the water vapor is now expressed with the moisture ratio, v D = n D n f L = n D n D + n L = n D / n L 1 + n D / n L = ξ 1 + ξ this results in the ratio of the gas constants and the molar masses

oder FfL = 1 - p"(TfL )p * ϕ From this follows for the expression sought which describes the influence of the air humidity on the injection duration

or F f L = 1 - p "(T f L ) p * ϕ

From the error propagation law follows for the relative error ΔF _{f L} / F _{f L} the moisture factor F _{f L} .DELTA.F f L F f L = ± p "(T f L ) * ϕ p - p "(T f L ) * ϕ * Ap 2 p 2 + Ap " 2 p " 2 + Δφ 2 φ 2

If the ambient pressure p = 1 bar and its relative error Δp / p = ± 3% is used, this is the range in which the ambient pressure usually fluctuates, for the relative humidity the greatest possible value ϕ = 1, with a realistic measurement inaccuracy of Δϕ = ± 10% and the relative error with which the saturation pressure is to be determined as Δp "/ p" = ± 5%, the result is F _f for the moisture influence factor _L and its relative error ΔF _{f L} / F _{f L} the values shown in the following table depending on the ambient temperature. T _{f L}
(° C) p "(T _{f L} )
(bar) F _{f L}
(-) ± F _{f L} / F _{f L}
(%) - 40 0.000124 0.99988 0.001434 - 30 0.000373 0.99963 0.004324 - 20th 0.001029 0.99897 0.011908 - 10th 0.002594 0.99741 0.030065 0 0.006107 0.99389 0.071031 10 0.012271 0.98773 0.143615 20 0.02337 0.97663 0.276622 30 0.04242 0.95758 0.512098 40 0.07375 0.92625 0.920432 50 0.12335 0.87665 1.626563 60 0.19920 0.80080 2.875564 70 0.31160 0.68840 5.232563

From the example calculation it can be seen that the influence of moisture at high ambient temperatures should not be neglected, but also that the errors at relative imprecise determination of the relative air humidity is not significant. In particular, an ambient pressure of p = 1 bar can be expected, so that a measurement of the ambient pressure can be omitted.

Claims (7)

1. Method for controlling internal-combustion engines taking account of the atmospheric humidity, in particular for motor vehicles, by means of at least one temperature sensor (1) and a sensor (2) for directly or indirectly recording the relative atmospheric humidity ϕ, comprising the following method steps:

   a) recording the temperature T_{f L} of the air and the relative atmospheric humidity ϕ,

   b) determining the saturation pressure p''(T_{f L} ) of the water vapour for the recorded temperature T_{f L}

   c) determining a correction factor Ff L = 1 - p"(TfL )p * ϕ where the total pressure p of the humid air is optionally assumed to be constant or additionally recorded, and

   d) determining an adapted fuel quantity, which is fed to the internal-combustion engine, by means of the correction factor F_{f L}
2. Method according to Claim 1, characterized in that the injection time for the fuel quantity is adapted by means of the correction factor F_{f L} .
3. Device for controlling internal-combustion engines, comprising a control unit (5), a temperature sensor (1) and a sensor (2) for directly or indirectly recording the relative atmospheric humidity ϕ, the temperature sensor (1) and the sensor (2) for recording the relative atmospheric humidity ϕ being arranged upstream of or in an intake section (10) of the internal-combustion engine, the sensor outputs being connected to the control unit (5) and the control unit (5) calculating the correction factor in accordance with step c from Claim 1 and adapting the fuel quantity to this correction factor.
4. Device according to Claim 3, characterized in that a pressure sensor (3) for recording the pressure p of the intake air is arranged upstream of or in the intake section.
5. Device according to Claim 4, characterized in that the pressure sensor (3) arranged upstream of the intake section is designed as a level-correction pressure sensor.
6. Device according to one of Claims 3 to 5, characterized in that the control unit (5) is assigned a memory component (4), in which the characteristic curve p''(T_{f L} ) of the saturation pressure of the water vapour is stored, which can then be used as defined in Claim 1.
7. Device according to one of Claims 3 to 5, characterized in that an algorithm is stored in the control unit (5), by means of which algorithm it is possible to calculate the saturation pressure p''(T_{f L} ) of the water vapour, so that it can then be used as defined in Claim 1.

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